N=input()
c=input()
print(c[:c.count('R')].count('W')) N=input() N input() input c=input() c input() input print(c[:c.count('R')].count('W')) print c[:c.count('R')].count('W') [:c.count('R')].count [:c.count('R')] c :c.count('R') c.count('R') c.count c count 'R' count 'W' c=input() input() c N=input() input() N
N=input()
c=input()
print(c[:c.count('R')].count('W'))
